Various methods of compressing data are known, and they are described, for example, in the book entitled "Compression de donnees--Methodes, algorithmes, programmes detailles" ["Data compression--methods, algorithms, detailed programs"] by Pascal Plume, published by Editions Eyrolles.
Among those methods, reference may be made to the "Huffman" method which acts on characters and which consists in encoding characters that occur relatively frequently over a binary length that is relatively short (compared with conventional binary encoding such as ASCII encoding, for example), and in encoding characters that occur less frequently over a binary length that is longer, the resulting encoding table being conveyed to the apparatus serving to perform the inverse, decompression operation.
Such a method is not suited to compressing messages, in particular in terms of compression ratio, since said words or said messages usually include repetitive sequences of characters.
To avoid that drawback, it is possible to use a method such as the "Lempel-Ziv-Welch" method which enables such repetitive sequences of characters to be compressed by replacing them with their ranks in an encoding table referred to as a "dictionary" and created dynamically as the text to be compressed is read, and recreated in similar manner on decompression. Such a method, also referred to as "on-line textual substitution" offers a better compression ratio than the above-mentioned method. Unfortunately, its main drawback is that it requires a decompression time that is relatively long.
A particular need therefore exists for a method of compressing messages, in particular a relatively large number of messages that are relatively short and that use a relatively limited vocabulary, such as, for example, messages intended to be displayed on the screen of equipment such as a telecommunications terminal, in particular a portable telephone. This need requires in particular a method that offers a decompression time that is sufficiently short while remaining sufficiently economical in terms of compression ratio.